It is known from the prior art that anthraquinone may be obtained on treating with air or oxygen a solution or dispersion of octahydro-anthraquinone (French Pat. No. 673,825 of Apr. 22, 1929). Another process comprises heating 1,4,4a,9a-tetrahydro-anthraquinone in the presence of nitrobenzene (British Pat. No. 895,620 of May 2, 1962). It is also possible to obtain anthraquinone by heating the 1,4,4a,5,8,8a,9a,10a-octahydro-anthraquinone in the presence of nitrobenzene, but the yield of the reaction is poor and the product obtained is not pure.